The goal of this FIRCA application is to develop and evaluate a new and direct assay of small airway function. In 1967 Macklem and Mead introduced the notion of the "silent zone" of the lung, those small airways of the lung periphery in which airways disease can progress undetected because they contribute little to total pulmonary resistance. To this day the detection and quantification of small airway function is at best a process that is indirect, inferential and nonspecific. This application deals with an innovative animal model which adapts alveolar capsule technology to that important question. On the basis of preliminary studies, the sensitivity and specificity of this approach appear to make it by far the best method available to investigate small airway function in situ. The parent grant, a program project, deals with the cascade of events that culminate in normal or abnormal pulmonary architecture, mechanics and gas transport.